The results add to evidence challenging the long-held belief that such cysts, which are sacs filled with fluid or other soft tissue, would trigger cancer.

But it will take longer follow-up “to definitively confirm these findings,” Dr. Usha Menon, of the University College London, and colleagues caution in a report in the journal BJOG.

According to the American Cancer Society, about 1 in 71 women get ovarian cancer at some point, with half of the cases occurring after age 60.

Data for the new study came from the UK Collaborative Trial of Ovarian Cancer Screening, which includes more than 200,000 women aged 50 to 74 years.

About half of those are getting ultrasound screening exams at regular intervals. In the first year, screening identified 1,234 women with inclusion cysts, and 22,914 with normal ovaries, according to the report.

After an average of six years, four women with cysts -- or about five in 1,000 -- and 32 with normal ovaries -- about one in 1,000 -- had developed ovarian cancer. Although that suggests increased risk, statistical tests showed that could easily have been due to chance.

The risks for other kinds of cancer weren’t reliably higher in women with cysts, either.

What’s more, the percentage of women with cysts who got cancer in the study was similar to what would have been expected in the general UK population, the research team reports.

“Our data,” they conclude, “show that ultrasound-detected inclusion cysts in postmenopausal women do not seem to be associated with an increased incidence of primary invasive ovarian or hormone-dependent cancers, such as breast and endometrium.”